Device for recording data on a medium, method implemented in such a device and recording medium obtained from said device

ABSTRACT

This device intended to record optical discs  5  comprises a control circuit for controlling the power of the recording laser beam  70  which takes a plurality of parameters into account notably the jitter of the recovered written data which is measured during the reading of recorded data which are produced by a reading block  71 . Furthermore, the power may be corrected as a function of the temperature inside the laser housing by measuring the threshold current at which the light is switched on. Other parameters used to correct the laser power take into account the scanning velocity of the disc and the amount of disc tilt. Application: Recording for CD (compact disc), DVD (digital versatile disc), BD (Blu-ray Disc).

The invention relates to a device for recording data on a recordingmedium which can be written by a recording head unit which produces arecording energy beam, the device comprising:

-   -   a control assembly for controlling the intensity of the        recording beam,    -   a set of measures for supplying control data to said control        assembly comprising a measuring circuit for measuring the level        of the recorded signals,    -   a database relating to the medium for supplying previous data to        said control assembly.

The invention has interesting applications notably in the recording ofoptical discs by means of laser beam pulses. Due to, on the one hand,various kinds of media involved and, on the other hand, mechanical,electrical, and optical imperfections of the recording devices, it isvery difficult to use predefined parameters for the laser pulses. It isthus necessary to make corrections. On this subject European patentdocument EP 0 762 399 may be consulted. In this document it is proposedto determine the power of the recording pulses on the basis of the levelof the recorded signal during a previous recording attempt.

However, it has turned out that, in many cases this determination is notsufficient for obtaining a recording of good quality. Besides themultitude of recordable and rewritable optical media available on themarket, each of them with particular characteristics, the recordingprocess is very much influenced by the ambient temperature, ageing ofthe semiconductor laser, or other factors that can not always bepredicted in a well-defined manner.

The present invention proposes a device of the type defined in theopening paragraph which thus permits to obtain a recording of goodquality while taking other measures into account than those relating tothe level of the recorded signal.

For this purpose, such a recording device is remarkable in that the setof measures comprises additional measuring circuits of the recordedsignal.

In a preferred embodiment the device is remarkable in that at least oneof the measuring circuit determines parameters through measurements fromreal time recording conditions.

The inventive idea consists of utilizing and managing a multiplicity ofparameters that includes not only those specified by media manufacturersbut also parameters established during previous recording stages thattook place on the same disc.

The invention also relates to a recording method which is characterizedin that it comprises the following steps:

-   -   insertion of a medium to be recorded,    -   identification of the medium,    -   rejection of the medium if it is unsuitable for recording,    -   test recording based on a set of default recording parameters,    -   reading of the test recording,    -   determining the recording power based on the level of the        recorded signals,    -   correcting of the recording power depending on the timing jitter        accompanying the recovered data,    -   correcting the recording power as a function of a plurality of        measured parameters notably the temperature,

It is possible to add steps for correcting the recording power as afunction of other measured parameters such as the disc velocity, theamount of disc tilt . . . .

The invention also relates to a recording medium which contains dataobtained via said method.

These and other aspects of the invention are apparent from and will beelucidated, by way of non-limitative example, with reference to theembodiment(s) described hereinafter.

In the drawings:

FIG. 1 shows a device in accordance with the invention,

FIG. 2 shows a diagram in explanation of the measures of the invention,

FIG. 3 shows how the power correction is evaluated as a function ofjitter,

FIG. 1 shows a device according to the invention referred to as 1. Thisdevice 1 is intended to record data on a recording medium 5 along aspiral-shaped winding track, for example. This medium is preferably anoptical disc whose optical properties are modified by means of a laserbeam pulse coming from an optoelectronic block 10. This block 10contains at least a laser diode (not shown in the Figure) for permittingthe recording of data on the optical disc 5 and also the reading of datawhich are recorded there. This exposé will also cover etched recordingoperations. The block 10 comprises a set of mechanisms for focusing thelaser beam to accurately follow the etched tracks and also to permit thedisplacement of this block. This displacement is represented by a motor11. The disc 5 is rotated by means of a motor 12. Reference 14 alsoindicates the motor used for the loading and unloading of the medium 5.The device according to the invention is managed by a microprocessorassembly 17. This assembly comprises inter alia a microprocessor 18 anda rewritable EEPROM memory referred to as 19. The data used and producedby this assembly 17 are transmitted over a common data line 25 (BUSline).

The signals coming from block 10 are first of all processed by a signalpre-processor 28. The signals coming from this processor aresubsequently processed by a format detector 30 which defines thestructure of the optical disc 5. This format detector supplies data to achannel decoder 32 which, inter alia, supplies data to a servocontrolgroup 35 for controlling the various slaves of the device alreadymentioned while also using data from the pre-processor 28. Before beingapplied to the motors, these signals are amplified by an amplifierassembly 40. A unit controls the power of the laser for engraving thedisc 5. The unit comprises a channel coder 36 followed by a writingstrategy circuit 37 and a laser power control circuit 38.

A processing block 45 connected to the line 25 permits the user toaccess various functionalities of the device. This is represented byterminal 50. This block utilizes a memory assembly 52. If needed, theretrieved data may also processed by an audio/video processor 54. Theprocessing block 45 comprises a coding/decoding circuit 56, a buffermemory management circuit 58 and an interface circuit 60 which ensures,inter alia, that the levels of the signals intended for this use aretaken into account.

FIG. 2 shows in diagrammatic manner the elements which are involved inthe invention. The elements common to those of the preceding Figurecarry like references. A block 70 is depicted which containsfunctionalities contained in the various elements shown in FIG. 1 whichensure the implementation of the invention. This block determines therecording laser beam power as a function of the various parameters whichare used by the invention.

-   Scanning speed of the laser spot as it proceeds from the inside of    the disc to its periphery.-   Jitter. Jitter is measured while taking into account the phase    errors that occur while synchronizing the regenerated binary data    with the regenerated clock frequency used as reference. FIG. 3 shows    how this jitter value determines a correction of the intensity of    the laser beam. Several consecutive recordings are performed with    increasing (or decreasing) laser powers starting from a previously    determined value P and by incremented this value in steps ΔP, not    necessarily equal to each other. For each of these power levels the    jitter Errφ is measured by reading out the recorded data. The value    P_(opt) _(—) _(g) is determined by interpolation, which gives the    minimum error. In the Figure the interpolation established by means    of straight lines D1 and D2 which best pass through the jitter    measuring points and whose intersection produces a value D_(opt)    (distance between the power changes which in its turn gives the    value of the power between two value increments). This value is    established on a straight power line DP_(W). Other methods for    finding the minimum jitter value may also be applied.-   Defects on disc. The recording power may need adjustment when the    laser beam has to pass through some defects present on the disc    surface, like fingerprints, in which case usually more power is    needed for writing.-   Temperature of the laser. The temperature can be estimated by    measuring the current supplied to the laser diode such that the    light is just switched on, which corresponds to the so-called bias    power. This current is fed to the laser diode by the laser driver    38. A power correction will be commanded as a function of the value    of this current. This process will be continued during the actual    recording phase by measuring the bias current between laser pulses.    Estimation of the laser temperature is, however, not limited to the    method described herein and may take place, for example, by using a    temperature sensor.

Determining the recording laser power involves either calibrationprocedures consisting of writing sequences of test patterns in dedicatedtest areas on disc or using the information recorded during normaloperation. The latter can be read out during the idle moments in whichthe optical unit does not receive data through the interface 50. As forthe test areas, the optical media standards provide at leat one such aresituated at the inner disc radius and, in some cases, a second test areasituated close to the disc edge.

The invention particularly relates to a power control procedure forcontrolling the emission of the laser beam called OPC (Optimal PowerControl). The operation of the device according to the inventiondescribed more particularly within the framework of optical discs,satisfying the various standards for recordable and rewritable CD andDVD media or any other optical media with recording characteristics.Example of such media are CD-R, CD-RW, DD-R, DD-RW, DVD-R, DVD-RW,DVD-RAM, DVD+R, DVD+RW, Blu-ray Disc, etc. The application of theinvention will be discussed below by means of an example, in particular,by showing how the laser power can be adjusted based on a multitude ofparameters in a DVD+R recorder. The following sequence of operations areperformed:

1 A start is made with the insertion of the medium (optical disc) 5.

2 The identification of this medium and also of its manufacturer issearched for.

3 Parameters stored in the lead-in area of the disc are recovered and,if there is no data whatsoever in this area, these parameters adoptdefault values.

4 Recovery of the recording parameters previously stored in the EEPROMmemory 19. The memory 19 has been loaded with such parameters duringprevious recording sessions that use discs of the same type and from thesame manufacturer. These parameters constitute thus a database in whichthe newly inserted optical disc 5 may be found.

5 Reading of the OPC counting location to determine the sequences to becarried out for a new power calibration procedure.

6 Execution of the OPC procedure.

7 Updating of the parameters in the EEPROM memory 19.

However, before proceeding with an OPC sequence on an optical disc whichhas just been inserted into the device, it is necessary to examine thefollowing possibilities:

A The inserted disc is fully blank, thus the procedure may be started innormal fashion.

B The inserted disc has been recorded partially and sufficient placeremains for carrying out at least a power calibration operation. The OPCprocedure will be executed and the parameters stored in the memory 19during a previous recording operation will also be used.

C Examination of the situation according to which a disc has alreadybeen written and there is no more place for carrying out an OPCprocedure. In the latter case a decision is to be made to know whether anew recording is made by means of at least certain parameters by defaultor whether the recording process is stopped.

D The inserted disc has been recorded completely and is recognized asbeing finalized. It is not necessary to start the etching operation.

Having available the various system information (e.g. identificationdata, recording parameters) and also the data contained in the EEPROMmemory 19, one proceeds with the reading of the OPC counting location.In this area the number of ECC blocks already used for previouscalibration procedures is found. The location PSN_(opc) _(—) _(start)from where the calibration sequence will start is determined,PSN _(opc) _(—) _(start)=23480+4×(27480−PSN _(icz) _(—) _(first)),where PSN_(icz) _(—) _(first) represents the physical address of thefirst empty sector of the counting area.Loading of Indicative Recording Parameters

If there are no indicative values related to the recording process on aparticular medium, values by default are admitted included in the EEPROMmemory 19. These values are chosen for a particular scanning velocity atwhich the disc has to be written. λ_(ind) _(—) _(def) P_(ind) _(—)_(def) β_(ind) _(—) _(def) [nm] K_(λ) _(—) _(def) [mW] 1X and 1X and 1Xand DVD + R support 1X 2.4X 2.4X 2.4X 2.4X Media manufacturer 10.0 15.00.08 655 10 no. 1 Media manufacturer 0.02 7 no. 2 Without indication0.05 8.5

The coefficients K_(λ) _(—) _(def) represent the normalized dependenceof the laser power taking the wavelength of the laser into account. Thenominal value is given by $\begin{matrix}{K_{\lambda} = {\frac{\mathbb{d}P}{\mathbb{d}\lambda} \cdot \frac{\lambda_{ind}}{P_{ind}}}} & (1)\end{matrix}$If one wishes to take the ambient temperature into account, a correctionmay be made using the following formula: $\begin{matrix}{P_{w} = {K_{x}\left\{ {P_{ind} + {K_{\lambda}{\frac{P_{ind}}{\lambda_{ind}}\left\lbrack {\lambda_{opu} - \lambda_{ind} + {K_{t}\left( {T_{a} - T_{s}} \right)}} \right\rbrack}}} \right\}}} & (2)\end{matrix}$

where the meaning of the symbols and their default values are given bythe table below. Default Parameters Symbol Value Unity Indicativerecording power at 1X P_(ind) Read from mW disc Recording overspeed(X-factor) K_(x) 1.2 — Dependence on the normalized laser K_(λ) Readfrom — power relative to the wavelength. disc Experimental correctionfor K_(λ) K_(exp) 1.5 — Initial laser wavelength at T_(s) λ_(opu) 663 nmIndicative wavelength at which the λ_(ind) Read from nm power P_(ind)has been measured. disc Drift of the wavelength due to K_(t) 0.2 nm/grdvariations of the ambient temperature. Ambient temperature T_(a) 40 ° C.Temperature at which the laser T_(s) 25 ° C. wavelength is specified.

The recording power expressed as a setpoint to be used by the laserdriver can be written in the form: $\begin{matrix}{P_{setpoint} = {P_{w} \cdot K_{grating} \cdot \frac{K_{loss}}{P_{nom}} \cdot P_{setpoint\_ nom}}} & (3)\end{matrix}$

in which expression: Value by Parameter Symbol default Unity Estimatedrecording power. P_(w) Cf Eq. (2) mW Factor due to partitioning of thelight K_(grating) 16/14 — bundle in more than one spots on discExperimental correction factor (due K_(loss) see below — to lightscatering or other factors. Nominal power of the laser for P_(nom) takenfrom mW calibration of the laser driver (19) Nominal power setpoint forAlpha_nom taken from — the laser driver. (19) DVD + R media K_(loss)Media manufacturer no. 1 1.000 Media manufacturer no. 2 0.950 Noidentification 0.975

A typical value of the nominal laser power for DVD+R media is P_(nom)=10mW. The correction coefficient K_(exp) is determined experimentally tocompensate for various losses in the light power due to, for example,scattering of the light upon entering the transparent substrate of thedisc. It compensates for the differences in the measurements made in thestart parameters VEMOS and in the recorders of the type DVD+R.

The laser power calculation may take even more variables into accountthan given in Equation (2). For example, two more coefficients K_(tilt)and K_(aberr) may be used to correct for the amount of disc tilt and theamount of aberrations in the optical system, respectively. The formula(2) will become then $\begin{matrix}{P_{w} = {K_{aberr}K_{tilt}K_{x}\left\{ {P_{ind} + {K_{\lambda}{\frac{P_{ind}}{\lambda_{ind}}\left\lbrack {\lambda_{opu} - \lambda_{ind} + {K_{t}\left( {T_{a} - T_{s}} \right)}} \right\rbrack}}} \right\}}} & (4)\end{matrix}$In addition, note that some parameters may also be adjusted in real timeduring recording and not only fixed during a calibration procedure thattakes place before recording. This is the case, for example, in datadrives that record at high speeds where the temperature inside the laserhousing may exhibit large variations during operation and the recordingspeed may change at various locations on disc. Alternatively, therecorder may check the written data during idle periods and determinecorrection factors based on a jitter measurement.

1. A device for recording data on a recording medium which can bewritten by a recording head unit which produces a recording energy beam,the device comprising: a control assembly for controlling the intensityof the recording beam, a set of measures for supplying control data tosaid control assembly comprising a measuring circuit for measuring thequality of the recorded signals, a database relating to the medium forsupplying previous data to said control assembly, characterized in thatthe set of measures comprises additional measuring circuits of therecorded signal.
 2. A device as claimed in claim 1, characterized inthat at least one of the measuring circuit determines parameters throughmeasurements from real-time recording conditions.
 3. A device as claimedin claim 1 or 2, characterized in that at least one of the measuringcircuits is a jitter measuring circuit.
 4. A device as claimed in claim1 or 2 or 3, characterized in that at least one of the measuringcircuits is a temperature measuring circuit that operates in real timeduring recording.
 5. A device as claimed in claim 4, characterized inthat the temperature measuring circuit is in the form of a circuit formeasuring threshold current needed by the semiconductor laser to whichon the light.
 6. A device as claimed in claim 1 to 5, characterized inthat at least one of the parameters supplied to the control controlassembly is related to the scanning velocity at which the recording takeplace.
 7. A device as claimed in claim 1 or 6, characterized in that atleast one of the measuring circuits is a tilt measuring circuit thatoperates in real time during recording.
 8. A device as claimed in one ofthe claims 1 to 7, characterized in that at least part of the databaseis contained at a location of said medium.
 9. A device as claimed in oneof the claims 1 to 8, characterized in that at least part of thedatabase is contained in one of its memory circuits.
 10. A device asclaimed in one of the claims 1 to 9, characterized in that the recordingmedium is in the form of an optical disc.
 11. A recording methodimplemented in a device as claimed in one of the claims 1 to 10,characterized in that it comprises the following steps: insertion of amedium to be recorded, identification of the medium, rejection of themedium if it is unsuitable for recording, test recording based on saidprevious data, reading of the test recording, determining the recordingpower based on the level of the recorded signals, entering a possiblecorrection of said recording power as a function of jitter data,entering a possible correction as a function of temperature, scanningspeed of the disc, the amount of disc tilt or any other parameter thatinfluences substantially the quality of the recorded data,
 12. A methodas claimed in claim 11, characterized in that the step relating to thecorrection as a function of temperature, scanning speed, or any otherparameter is carried out in real time during the recording of data. 13.A recording medium obtained by the implementation of the method asclaimed in one of the claims 11 or
 12. 14. A recording medium as claimedin claim 13, characterized in that it is in the form of an optical disc.